This invention relates to a control system for a hydraulically driven vehicle.
A hydraulically driven vehicle is generally provided with a pair of independent closed loops each for driving one side of tracks or wheels of the vehicle. Each closed loop includes a variable displacement hydraulic pump driven by a prime mover such as an engine and a fixed displacement or variable displacement hydraulic motor driven by the variable displacement hydraulic pump. Displacement volume of each variable displacement hydraulic pump is controlled by changing the angle of a swash plate, which is controlled and operated by a servo valve.
Each servo valve is controlled by a servo control valve means comprising a pressure regulator and a directional control valve for a forward and reverse change-over. Both the pressure regulator and the directional control valve are operated by a speed control lever. By manipulating the speed control lever, the speed of the vehicle and the forward and reverse change-over can be realized. In a conventional hydraulically driven vehicle, however, since speed of the vehicle is controlled by manipulating the speed control lever, speed control of the vehicle becomes troublesome where a frequent starting and stopping operation of the vehicle is required for the driver. It has also been difficult to attain the same speed of the vehicle as the previous speed after the vehicle is stopped and restarted since speed of the hydraulically driven vehicle is generally changed infinitely.